This invention generally relates to an arrangement for concentrically positioning first and second parts relative to one another, particularly a casing, sleeve, or bushing, relative to a shaft, wherein the parts are made of materials with different coefficients of thermal expansion.
In many instances it is desirable, when positioning parts concentric to one another, to use parts made from various materials with, accordingly, different reactions to changing temperatures. For example, it is often desired to make a bearing sleeve, or journal, of a journal bearing from a wear-resistant material, for example a ceramic, for reducing wear thereof. When such a ceramic bearing sleeve operates, or rotates, together with a component, for example a shaft, made from a type of steel, problems arise because a coefficient of thermal expansion for steel is a multiple of times higher than that of ceramic; thus risking that the bearing sleeve will break when it is used at higher temperatures because of the greater thermal expansion of the metal part. A similar problem arises in low temperatures when ceramic materials hinder shrinkage of attached metal. Therefore, it has been suggested in the prior art to provide O-ring shaped centering elements between a bearing sleeve and a shaft which allow an expansion of the metal shaft relative to the ceramic bearing sleeve. This solution has the disadvantage that, in addition to providing low thermal tolerances of the centering elements, usually insufficient concentric alignment along an axial length of the bearing sleeve is accomplished, which is often unacceptable, because this may cause wear and premature failure at other locations in the overall equipment or machine. It is known from the prior art to arrange so-called tolerance bands between bearing sleeves and shafts, that is, bands having wave-shaped cross sections, thereby having spring characteristics in radial directions. Accuracy of concentric alignment by means of such tolerance bands is also not satisfactory. Further, premature failure of such a bearing sleeve may occur because of high localized wear at those places where the tolerance bands and the bearing sleeve touch. A similar arrangement is disclosed in German patent document DE-C-37 06 365 which discloses a sleeve-shaped middle, or intermediate, part having protruding tongue-shaped portions which are cut out of the middle part in a cost-intensive manufacturing process (laser cutting method), to be positioned between the parts to be centered. In addition to the aforementioned disadvantages, this solution is cost-intensive and appears to create problems during assembly thereof.
It is an object of this invention to provide an apparatus, or assembly, of a type mentioned above which can withstand thermal stress and which allows precise concentric alignment of parts with different thermal expansion reactions with the expenditure of comparatively low technical effort and costs.